There are games wherein a player operates a player character to bring down an enemy character by using a virtual gun or sword in a virtual game space. For example, when an enemy character appears, the player moves the player character to the position or aims at the position to bring the enemy character down. Sometimes the player character is not allowed to advance if the player character is found by the enemy character, unless the player character brings the enemy character down. In many games, when the player character brings down an enemy character, a different enemy character newly appears, and the game is not completed unless the player character brings down the enemy characters that appear one after the other. Game devices cause suitable new enemy characters to appear in accordance with factors such as the position and level of the player character, so as to provide a more interesting development of game and attract the interest of the player. For example, Patent Literature 1 discloses a game system wherein factors such as the number and strength of the enemy characters are controlled based on the number of players participating in the game and the level of the player characters, thereby increasing the interest of the game without greatly reducing game balance.    Patent Literature 1: Unexamined Japanese Patent Application KOKAI Publication No. 2004-160059